Here is a closeup wireframe of the window. I have marked it with red X's to indicate places where edges or vertices are NOT welded, and green circles to show where edges *are* welded.

Because the curves are welded, they render beautifully smooth in Poser with smoothing on. But where I don't want those artifacts produced by curved joings in the corners of the window pains, they are not welded.

The result is a great reduction in poly and vertex count, without any artifacts in Poser.

You wanted to know how to model for Poser - this is how and why.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)